A Finite Element Formulation for the Large Deflection Random Response of Thermally Buckled Structures

The effects of temperature and acoustic loading are included in a theoretical finite element large deflection formulation for thin, isotropic plate and beam type structures. Thermal loads are applied as steady-state temperature distributions, and acoustic loads are taken to be stationary and Gaussian with zero mean and uniform magnitude and phase over the surface of the structure. Material properties are considered to be independent of temperature. Also, inplane and rotary inertia terms are assumed to be neglegible, and all inplane edge conditions are taken to be immovable. For the random vibration analysis, cross correlation terms are included. The nature of the loads leads to the solution of two separate problems. First, the problem of thermal postbuckling is solved to determine the deflections and stresses due to the thermal load only. These deflections and stresses are then used as initial deflections and stresses for the random vibration analysis. Since both analyses are nonlinear, iterative techniques are used to solve each. The solution technique used for the thermal postbuckling analysis is that of Newton-Raphson iteration. This method is found to always converge; whereas, direct iteration fails to converge. For the large deflection random vibration analysis, the linear mode shapes of the thermally buckled structure are used to reduce the equations of motion to a system of nonlinear modal equations. An equivalent linearization technique is then used to iteratively solve for the mean square deflections. Instead of using direct iteration, an underrelaxation technique is employed to reduce the number of iterations required for a converged solution. In addition to obtaining mean square deflections, the boundary for stable random vibrations for the thermally buckled structure (snap-through boundary) is predicted by considering the incremental equations of motion. Solutions obtained using these analysis methods are compared with previous solutions to assess the accuracy of the finite element formulation. The thermal postbuckling solution is compared with a 25-mode classical solution for a square plate clamped on all edges, and the random vibration solution is compared with 100-mode classical beam solutions. The present study shows that the infinite element method can be used to analyze structures subjected to combined thermal-acoustic loads

Acoustic power flow into the ear and the auditory microstructure

An experimental technique to determine the acoustic power absorbed by the human ear at absolute threshold is described and applied to data recorded in adult subjects. A previously published method of electroacoustic probe calibration in terms of equivalent Thevenin source parameters is substantially ameliorated. Careful and detailed measurements of continuous tonal aural sound pressure (CTASP) are presented. Ear canal input impedance, reflectance and absolute power flow constituents are derived from CTASP data. Auditory microstructure, characterised by spectral periodicity, is observed and validated in CTASP, impedance, reflectance and power flow parameters at a 20 dB SPL stimulus level, but undetectable at 60 dB SPL. Periodicity in the ear canal acoustic parameters elicited at low stimulus levels is found to be commensurate with absolute threshold microstructure. An elementary analogue network model of the peripheral auditory system is formulated, enabling cochlear input impedance and reflectance to be inferred from ear canal acoustic parameters. At a 20 dB SPL stimulus level a non-zero cochlear reflectance is inferred, implying that energy propagates basally, as well as, apically. Microstructure amplitude in cochlear input impedance is shown to be 4 dB greater than that in ear canal input impedance, a consequence of decoupling of the probe from the tympanic membrane. A proportionality between transmittance and auditory sensitivity exists, implying that the ear couples more efficiently to the sound source, and consequently extracts proportionally more power, at peaks in sensitivity. However, the measured change in coupling is inadequate to wholly explain threshold microstructure. An explanation is offered by applying empirical data to a phenomenological model of power flow within the peripheral auditory system. It is argued that threshold microstructure arises predominately from a phasic interaction of the basalward and apical travelling waves effectively modifying the spatial distribution of energy within the cochlea

Management of Asymptomatic Renal Stones in Astronauts

Introduction: Management guidelines were created to screen and manage asymptomatic renal stones in U.S. astronauts. The risks for renal stone formation in astronauts due to bone loss and hypercalcuria are unknown. Astronauts have a stone risk which is about the same as commercial aviation pilots, which is about half that of the general population. However, proper management of this condition is still crucial to mitigate health and mission risks in the spaceflight environment. Methods: An extensive review of the literature and current aeromedical standards for the monitoring and management of renal stones was done. The NASA Flight Medicine Clinic's electronic medical record and Longitudinal Survey of Astronaut Health were also reviewed. Using this work, a screening and management algorithm was created that takes into consideration the unique operational environment of spaceflight. Results: Renal stone screening and management guidelines for astronauts were created based on accepted standards of care, with consideration to the environment of spaceflight. In the proposed algorithm, all astronauts will receive a yearly screening ultrasound for renal calcifications, or mineralized renal material (MRM). Any areas of MRM, 3 millimeters or larger, are considered a positive finding. Three millimeters approaches the detection limit of standard ultrasound, and several studies have shown that any stone that is 3 millimeters or less has an approximately 95 percent chance of spontaneous passage. For mission-assigned astronauts, any positive ultrasound study is followed by low-dose renal computed tomography (CT) scan, and flexible ureteroscopy if CT is positive. Other specific guidelines were also created. Discussion: The term "MRM" is used to account for small areas of calcification that may be outside the renal collecting system, and allows objectivity without otherwise constraining the diagnostic and treatment process for potentially very small calcifications of uncertain significance. However, a small asymptomatic MRM or stone within the renal collecting system may become symptomatic, and so affect launch and flight schedules, cause incapacitation during flight, and ultimately require medical evacuation. For exploration class missions, evacuation is unlikely. The new screening and management algorithm allows better management of mission risks, and will define the true incidence of renal stones in U.S. astronauts. This information will be used to refine future screening, countermeasures and treatment methods; and will also inform the needed capabilities to be flown on exploration-class missions

Deceleration-Limiting Roadway Barrier

Roadway barrier system and method are disclosed for decelerating a moving vehicle in a controlled manner and for retaining the decelerated vehicle. A net or mesh of the roadway barrier system receives and captures the moving vehicle. The net or mesh is secured to anchors by energy absorbing straps. The energy absorbing straps deploy under a tensional load to decelerate the moving vehicle, the straps providing a controlled resistance to the tensional load over a predefined displacement or stroke to bring the moving vehicle to rest. Additional features include a sacrificial panel or sheet in front of the net that holds up the net or mesh while deflecting vehicles that collide only tangentially with the roadway barrier system

Microbial individuality: how single-cell heterogeneity enables population level strategies.

Much of our knowledge of microbial life is only a description of average population behaviours, but modern technologies provide a more inclusive view and reveal that microbes also have individuality. It is now acknowledged that isogenic cell-to-cell heterogeneity is common across organisms and across different biological processes. This heterogeneity can be regulated and functional, rather than just reflecting tolerance to noisy biochemistry. Here, we review recent advances in our understanding of microbial heterogeneity, with an emphasis on the pervasiveness of heterogeneity, the mechanisms that sustain it, and how heterogeneity enables collective function.The research has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement 338060. The work in the Locke laboratory is also supported by a fellowship from the Gatsby Foundation (GAT3273/GLC).This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.mib.2015.01.00

Using movies to analyse gene circuit dynamics in single cells

Many bacterial systems rely on dynamic genetic circuits to control crucial biological processes. A major goal of systems biology is to understand these behaviours in terms of individual genes and their interactions. However, traditional techniques based on population averages 'wash out' crucial dynamics that are either unsynchronized between cells or are driven by fluctuations, or 'noise', in cellular components. Recently, the combination of time-lapse microscopy, quantitative image analysis and fluorescent protein reporters has enabled direct observation of multiple cellular components over time in individual cells. In conjunction with mathematical modelling, these techniques are now providing powerful insights into genetic circuit behaviour in diverse microbial systems

NASA Screening and Clinical Practice for the Monitoring and Mitigation of Coronary Artery Disease: Application to Terrestrial Practice

Coronary artery disease (CAD) surveillance has led to the development of risk stratification tools that drive clinical mitigation efforts for CAD risk. As common risk assessment tools, including the Framingham Risk Score (FRS) or Pooled Cohort Risk Equations, have insufficient accuracy on an individual level to meet NASAs stringent screening guidelines, NASA has required new approaches to address the risk of catastrophic cardiovascular (CV) medical events among astronauts. Coronary artery calcium (CAC) scanning has emerged as the current best tool to enhance CV risk assessment in asymptomatic individuals, with risk information incremental to FRS data

Safer Roadside Crash Walls Would Limit Deceleration

The figure depicts the aspects of a proposed deceleration-limiting design for crash walls at the sides of racetracks and highways. The proposal is intended to overcome the disadvantages of both rigid barriers and kinetic-energy-absorbing barriers of prior design. Rigid barriers can keep high-speed crashing motor vehicles from leaving roadways and thereby prevent injury to nearby persons and objects, but they can also subject the occupants of the vehicles to deceleration levels high enough to cause injury or death. Kinetic-energy-absorbing barriers of prior design reduce deceleration levels somewhat, but are not designed to soften impacts optimally; moreover, some of them allow debris to bounce back onto roadways or onto roadside areas, and, in cases of glancingly incident vehicles, some of them can trap the vehicles in such a manner as to cause more injury than would occur if the vehicles were allowed to skid along the rigid barriers. The proposed crash walls would (1) allow tangentially impacting vehicles to continue sliding along the racetrack without catching them, (2) catch directly impacting vehicles to prevent them from injuring nearby persons and objects, and (3) absorb kinetic energy in a more nearly optimum way to limit decelerations to levels that human occupants could survive

Determining Optimal Levels of Nitrogen Fertilizer Using Random Parameter Models

The parameters of yield response functions can vary by year. Past studies usually assume yield functions are nstochastic ‘‘limited’’ stochastic. In this study, we estimate rye– ryegrass yield functions in which all parameters are random. The three functional forms considered are the linear response plateau, the quadratic, and the Spillman-Mitscherlich. Nonstochastic yield models are rejected in favor of stochastic parameter models. Quadratic functional forms fit the data poorly. Optimal nitrogen application recommendations are calculated for the linear response plateau and Spillman-Mitscherlich. The stochastic models lead to smaller recommended levels of nitrogen, but the economic benefits of using fully stochastic crop yield functions are small because expected profit functions are relatively flat for the stochastic yield functions. Stochastic crop yield functions provide a way of incorporating production, uncertainty into input decisions.cereal rye–ryegrass, Monte Carlo, nitrogen, random parameters, stochastic plateau, Production Economics, Q10, C12, D24,